Dielectric ceramic composition, ceramic capacitor using the composition and method of producing thereof

ABSTRACT

The present invention provides a dielectric ceramic composition, a capacitor using the composition and the producing method, of having a lower dielectric loss and a stable characteristics in high frequency bandwidth, and enabling to use a base metal or a carbon-based material as an electrode material by allowing sintering at a low temperature, thereby resulting in lower cost. The dielectric ceramic composition according to present invention, is characterized in comprising a main component of formula Sr x Mg 1-x (Xr y Ti 1-y ) O 3  (where 0.8≦x≦1; 0.9≦y≦1) to which MnO 2  of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi 2 O 3 , PbO and Sb 2 O 3  and a glass component of 0.5-15 wt % are added based on the weight of the main component.

BACKGROUND OF THE INVENTION

The present invention relates to a dielectric ceramic composition, moreparticular to a dielectric ceramic composition, a ceramic capacitorusing the composition and the producing method, thereof having a lowerdielectric loss and stable characteristics in high frequency bandwidth,and enabling to use a base metal(e.g. Cu, W etc.) or a carbon-basedmaterial as an electrode material by allowing sintering at a lowtemperature, and thereby reducing the production cost.

Conventionally, a dielectric property of a ceramic provides a ceramiccapacitor having larger capacitance and being more miniature in size.The ceramic capacitor may be made of a material selected from TiO₂having a rutile structure, BaTiO₃, MgTiO₃, CaTiO₃ and SrTiO₃, having aperovskite structure and the mixture thereof.

This ceramic capacitor may be classified into a platelike type and alaminate type. The platelike type capacitor is produced by forming saidmaterial powder into some shaped body, such as pellet(disc),rod(cylinder) or chip(angular), under pressure, sintering the shapedbody at 1200° C.-1400° C. to a sintered body, and forming electrode ateach surface of the sintered body.

Also, the laminated type ceramic capacitor is produced by mixing saidmaterial powder with organic binder and organic solvent to prepare aslurry, forming green sheets from the slurry through a doctor bladding,printing the pattern of electrode comprising of a noble metal, such asPt and Pd, on each of the green sheets, subsequently laminating saidgreen sheets in the thickness direction under pressure to form alaminate, and sintering the laminate at 1200° C.-1400° C.

As described above, however, in the conventional ceramic capacitor, thesintering process must be performed at a high temperature ranging 1200°C.-1400° C., to obtain the sintered body exhibiting a good electriccharacteristics and having a high density.

For the laminated ceramic capacitor, particularly, in the case of usinga base metal as an electrode material, there has been a problem tooxidize the base metal during the sintering process, which occurs a highresistance layer formation between the ceramic layers. To avoid theproblem, the noble metal material, being stable at high temperature,must be employed as an electrode material, thereby resulting in highcost.

On application of a device for high frequency bandwidth, such asmicrowave, it is preferred to have a low dielectric loss. And suchdevice is required to have a good electric characteristics such as aquality value(Q), temperature property(this term means temperaturechanging ratio of the capacity), and a high reliability. However, nocurrent dielectric material meets all the conditions.

Accordingly, there has been a need in the art to provide a dielectricceramic composition, ceramic capacitor using the composition and theproducing method to solve the problem as described above.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a dielectric ceramiccomposition and a producing method of the dielectric ceramic compositionof having a lower dielectric loss and a stable characteristics in highfrequency bandwidth, and enabling to use a base metal, such as Cu and W,or a carbon-based material as an electrode material by allowingsintering at a low temperature, thereby reducing the production cost.

To achieve the above object, the present invention provides thedielectric ceramic composition comprising a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1) to which0.05-15 wt % of MnO₂, 0.001-5 wt % of at least one selected from thegroup consisting of Bi₂O₃, PbO and Sb₂O₃ and 0.5-15 wt % of a glasscomponent are added based on the weight of the main component.

It is another object of the present invention to provide a ceramiccapacitor using the composition and a method of manufacturing theceramic capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention and wherein:

FIG. 1 illustrates cross-sectional structural views of a platelikeceramic capacitor in accordance with example 1.

FIG. 2 illustrates cross-sectional structural views of a laminatedceramic capacitor in accordance with example 2.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, the dielectric ceramic compositionis characterized in comprising a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))₃ (where 0.8≦x≦1; 0.9≦y≦1), to which MnO₂of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of 0.5-15 wt %are added based on the weight of the main component.

In the preferred embodiment, the dielectric ceramic composition isproduced by adding MnO₂ of 0.5-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glasscomponent 0.5-15 wt % based on the weight of the component to a maincomponent of formula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1;0.9≦y≦1). The resulting composition can exhibit a high dielectricconstant, a good temperature property and a high quality value(Q). As aresult, the dielectric ceramic composition is suitable for using at highfrequency bandwidth.

The mole fraction of Sr is preferably 0.8(80 mol %) or more, when thecomposition containing Sr of less than 0.8 is fired at 925° C.-1080° C.The sintering property of the resultant is deteriorated.

The mole fraction of Ti is preferably 0.1(10 mol %) or less. When themole fraction of Ti is more than 0.1, the temperature property as wellas the quality factor(Q) are deteriorated.

MnO₂ is added to the main component as a sintering aid agent forenabling to sinter at a low temperature. The amount of the agent ispreferably 0.05-15 wt %. When the amount of MnO₂ is less than 0.05 wt %,it does little function as an additive, resulting in a lower density ofthe sintered body. When the amount of MnO₂ is more than 15 wt %, thequality value is deteriorated.

A metal oxide having a low melting point is added to the main componentfor improving the temperature property. The metal may be at least oneselected from the group consisting of Bi₂O₃, PbO and Sb₂O₃. The additiveamount is preferably 0.001-5 wt %. When the additive is less than 0.001wt %, the temperature property cannot be improved. When the additive ismore than 5 wt %, the quality value is deteriorated.

The glass component is added thereto as a sintering aid agent forenabling to sinter at a low temperature. The additive amount ispreferably 0.5-15 wt %. When the glass component is less than 0.5 wt %,the temperature property cannot be improved. When the glass component ismore than 15 wt %, the quality value is deteriorated.

The glass component employed in the present invention preferably has agood wettability to the main component Sr_(x)Mg_(1-x)(Zr_(y)Ti_(l-y))O₃(where 0.8≦x ≦1; 0.9≦y≦1) and is softened and/or melted at 925-1080° C.Specifically, such glass component may be ZnO—SiO₂ based glass orLi₂O—Al₂O₃—SiO₂ based glass.

In second embodiment of the present invention, SiO₂ of 0.01-5 wt % andAl₂O₃ of 0.01-5 wt % based on the weight of the main component arefurther added to the dielectric ceramic composition to provide anotherdielectric ceramic composition.

SiO₂ is used as an additive for improving the temperature property. Theamount of SiO₂ is preferably about 0.01-5 wt %. When the amount of SiO₂is less than 0.01 wt %, the temperature property cannot be improved.When the amount of SiO₂ is more than 5 wt %, the quality value isdeteriorated.

Al₂O₃ is used as an additive for improving the quality value. The amountof Al₂O₃ is preferably about 0.01-5 wt %. When the amount of Al₂O₃ isless than 0.01 wt %, the quality value cannot be improved. When theamount of Al₂O₃ is more than 5 wt %, the temperature property isdeteriorated.

In the third embodiment of the present invention, a rare earth oxide of0.001-2 wt % is further added to the dielectric ceramic composition toprovide another dielectric ceramic composition based on the weight ofthe main component.

The rare earth oxide is used as an additive for improving thetemperature property. Preferably, the amount of the rare earth oxide isabout 0.001-2 wt %. When the amount of the rare earth oxide is less than0.001 wt %, the temperature property cannot be improved. When the amountof the rare earth oxide is more than 2 wt %, the quality value isdeteriorated.

The rare earth oxide employed in the present invention has preferably agood wettability to the main compositionSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1) and has agrain boundary layer, which is used to improve the sintering property.Specifically, such rare earth oxide may include at least one selectedfrom the group consisting of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃,Ho₂O₃, Er₂O₃, Tm₂O₃ and Yb₂O₃.

Also the present invention provides a ceramic capacitor with the opposedsurfaces comprising one of the dielectric ceramic compositions asdescribed above, each of which an electrode is formed on. The electrodeof the ceramic capacitor may be base metal or carbon-based material,since the capacitor can be produced through sintering at the lowtemperature.

Further, the present invention provides a ceramic capacitor made bylaminating alternatively electrodes and sheets comprising one of thedielectric ceramic compositions as describe above.

The ceramic capacitor according to the present invention exhibits alower dielectric loss and stable characteristics, by using one of thedielectric ceramic compositions as describe above. Therefore, theceramic capacitor is expected to have more improved reliability.Moreover, it is advantageous that the dielectric ceramic composition canbe sintered at a low temperature of 925-1080° C. Therefore, aninexpensive metal, such as a base metal and a carbon-based material, canbe used as an internal electrode, thereby reducing the production cost.

The base metal having a good conductibility and a high reliability ispreferably employed as the electrode, which may be at least one selectedfrom the group consisting of Cu, Ni, W and Mo, and the carbon-basedmaterial employed as the electrode may be carbon(amorphous), graphite orthe mixture.

In present invention, a ceramic capacitor fabricating method comprisesthe steps of forming powder comprising a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1), to which MnO₂of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of 0.5-15 wt %are added based on the weight of the main component, into a bulk or asheet; and sintering the bulk or a sheet at about 925-1080° C.

According to the method, a sintering aid agent of MnO₂ and glasscomposition can improve a wettability of a grain boundary layer to bindpowder particles and reduce the void fraction during the sinteringprocess even at low temperature of about 925-1080° C. Thus, the sinteredbody having a high strength and high density can be obtained at the lowtemperature.

In another embodiment of the present method, the method may comprise theadditional step of providing an electrode on a main surface of thesheet; laminating the sheet in the thickness direction under pressure toform a laminate; and sintering the laminate at about 925-1080° C.

According to this method, a base metal, such as Cu and Ni, or acarbon-based material, such as amorphous carbon and graphite, is used asan internal electrode, which is less expensive than noble metal, such asPt and Pd, resulting in the lower cost without deteriorating thecharacteristics.

The embodiments of the present invention will now be described by way ofexample.

EXAMPLE 1

Referring to FIG. 1, cross-sectional structural view of a platelikeceramic capacitor in accordance with a first example is shown in FIG. 1.The capacitor comprises a bulk shape dielectric body 1, terminalelectrodes 2 formed on the opposed surfaces of the dielectric body 1,lead lines 3 connecting to the terminal electrode, and an epoxy resin 4encapsulating the dielectric body 1 and the terminal electrode 2.

The dielectric body 1 is made of a dielectric ceramic compositioncomprising a main component of formula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃(where 0.8≦x≦1; 0.9≦y≦1), to which MnO₂ of 0.05-15 wt %, at least one of0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃and a glass frit(glass component) of 0.5-15 wt % are added based on theweight of the main component.

The dielectric body 1 may include one of to the dielectric ceramiccomposition further containing SiO₂ of 0.01‥5 wt % and Al₂O₃ of 0.01-5wt %, the dielectric ceramic composition further containing a rare earthoxide of 0.001-2 wt %, and the dielectric ceramic composition furthercontaining SiO₂ of 0.01-5 wt %, Al₂O₃ of 0.01-5 wt % and rare earthoxide of 0.001-2 wt %.

The terminal electrode 2 comprises a conductive material having a highreliability, such as Ag and Ag alloy. Preferably, Ag alloy may include90 Ag-10 Pd. The material of the terminal electrode 2 may also includeat least one selected from the group consisting of Cu, Ni, W and Mo, orcarbon, graphite or the mixture.

This ceramic capacitor exhibits a stable dielectric constant(ε), qualityfactor(Q) and temperature property (Tc) even in high frequencybandwidth.

The method of manufacturing this capacitor will now be described.

Each of Powdered SMZT, MnO₂, at least one selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, glass frit, SiO₂, Al₂O₃ and rareearth oxide were weighed as the predetermined amount.

In this example, each of powderedSr_(0.95)Mg_(0.05)(Zr_(0.95)Ti_(0.05))O₃, MnO₂, PbO, glasscomponent(ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass), SiO₂,Al₂O₃ and La₂O₃ was weighed to prepare a dielectric ceramic compositionas shown in Table 1.

TABLE 1 Main component Additive B (mole fraction) Additive A (wt %)Sintering Sr_(x)Mg_(1−x)(Zr_(y)Ti_(1−y))O₃ (wt %) Glass temperatureSpecimen Sr Mg Zr Ti MnO₂ Al₂O₃ SiO₂ frit PbO La₂O₃ (° C.) 1 1 0 1 0 00 0 0 0 0 1050  2 1 0 1 0 0.3 0 0 0.5 1.0 0 1000  3 1 0 1 0 0.3 0 0 3.01.0 0 950 4 1 0 1 0 0.3 0 0 11.0 1.0 0 950 5 1 0 0.95 0.05 5.0 0.1 0.052.5 0.5 0.01 950 5 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 1000  7 1 00.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 900 8 1 0 0.95 0.05 5.0 0.1 0.052.5 6.0 0.01 950 9 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 950 10 0.980.02 0.95 0.05 5.0 0.05 0.05 2.5 0.5 0.01 950 11 0.98 0.02 0.95 0.05 6.00.5 0.05 2.5 0.5 0.01 950 12 0.98 0.02 0.95 0.05 5.0 0.5 0.05 2.5 1.00.01 900 13 0.98 0.02 0.95 0.05 5.0 0.5 0.05 11.0 1.0 0.01 950 14 0.980.02 0.95 0.05 5.0 5.0 0.05 2.5 0.5 0.01 950 15 0.98 0.02 0.95 0.05 5.00.1 0.5 2.5 0.5 0.01 950 16 0.95 0.05 0.95 0.05 0.04 0 0 3.5 0 0 92517 0.95 0.05 0.95 0.05 2.5 0 0 0.4 0 0 925 18 0.95 0.05 0.95 0.05 2.5 00 3.5 0 0 925 19 0.95 0.05 0.95 0.05 3 0.2 0.3 0.4 0.5 0.00 950 200.95 0.05 0.95 0.05 5 0.1 0.05 5 0.5 0.00 900 21 0.95 0.05 0.95 0.05 50.1 0.05 5 0.5 0.03 950 22 0.95 0.05 0.95 0.05 5 0.05 0.05 5 0.5 0.03975 23 0.95 0.05 0.95 0.05 5 0.5 0.05 5 0.5 0.03 975 24 0.95 0.05 0.950.05 5 5.0 0.05 5 0.5 0.03 975 25 0.95 0.05 0.95 0.05 5 0.1 0.5 5 0.50.03 975 26 0.95 0.05 0.95 0.05 5 0.1 5.0 5 0.5 0.03 975 27 0.95 0.050.95 0.05 5 0.1 0.1 5 0.5 0.03 1050  28 0.8 0.2 0.95 0.05 5 0.1 0.05 3.50.5 0.03 950 29 0.8 0.2 0.95 0.05 5 0.1 0.05 5 0.5 0.03 900 30 0.750.25 0.95 0.05 5 0.1 0.05 5 0.5 0.03 950 comparison

The prepared components were wet-milled with water(or organic solventsuch as ethanol and acetone) in ball mill for predetermined time, suchas 24 hours. The resultant mixture was dehydrated(or removal of thesolvent, such as ethanol and acetone) and dried. Specimen comprisingdifferent composition from thereof the present invention was prepared ascomparison(indicated by in the Table 1).

Then, the dried mixture was preliminary fired at 550-750° C., for0.5-5.0 hours, followed by pulverizing for 1-24 hour with a mortarmachine(or automatic pestle) to obtain the fired powder having thedesired granularity.

Subsequently, an appropriate amount of an organic binder was added tothe fired powder. The resultant was mixed and granularized uniformlyusing a mortar machine and a like to obtain granular powder having thedesired granularity. Polyvinyl alcohol(PVA) was employed as a organicbinder. Other organic binder may include ethylcellulose aqueous solutionand acryl resin solution(acryl binder).

Then, the pellet having a diameter of 20 mm and a thickness of 0.5 mm isformed from the granular powder using a forming machine, followed byfiring at 925-1080° C., for 0.5-10 hours under atmosphere, to obtain adisk-shaped dielectric body 1.

The composition of the present invention was fired at the othertemperature to prepare another specimen as comparison(indicated by “” inthe Table 1).

Table 2 shows electric characteristics of each specimen, and thecomparison is indicated by “”.

TABLE 2 Temperature Dielectric Quality property Specimen constant valueResistance (Tc) number (ε) (Q) (Ω · cm) (ppm/° C.)  1* 13  230 1.6 ×10¹¹ 96  2 19  950 1.3 × 10¹² 93  3 23 2300 1.9 × 10¹² 60  4* 22  3801.5 × 10¹² 180   5 28 2680 1.7 × 10¹² 58  6 27 3630 1.5 × 10¹² 63  7* 24 190 1.6 × 10¹² 56  8* 33  180 1.5 × 10¹² 26  9 31 6000 2.0 × 10¹² 35 1029 2670 1.8 × 10¹² 38 11 27 2980 1.6 × 10¹² 32  12* 12  310 1.5 × 10¹²15  13* 28  60 1.8 × 10¹² 27 14 26  790 1.9 × 10¹² 43 15 25 2340 2.0 ×10¹² 36  16* 18  370 1.9 × 10¹² 32  17* 16  270 2.1 × 10¹² 27 18 23 25601.8 × 10¹² 68  19* 12  320 1.6 × 10¹² 71  20* 17  150 1.3 × 10¹¹ 29 2125 1700 2.2 × 10¹² 75 22 25 2550 2.1 × 10¹² 58 23 22 2500 1.7 × 10¹² 8224 26 2700 1.1 × 10¹³ 105  25 24 2300 1.9 × 10¹² 74 26 22 1970 1.5 ×10¹² 23 27 23 2200 2.1 × 10¹² 63 28 17 1290 2.0 × 10¹² 32  29* 12  2001.8 × 10¹² 17  30* 11  170 1.9 × 10¹² 40 *comparison

Wherein, the dielectric constant(ε) was measured at 25° C. under thecondition of frequency of 1 MHz and an input voltage of 1 V_(rms). The Qvalue was measured under the condition of frequency of 1 MHz and aninput voltage of 1 V_(rms). The temperature property (Tc) was calculatedfrom the following equation

Tc(ppm° C.)=(C2−C1×10⁶)/(C1×(125-25))

Wherein, the C1 is the capacitance at 125° C. and the C2 is thecapacitance at 25° C.

And the resistance (R(γ·cm)) was calculated by using the voltage and thecurrent, which were measured on applying a direct voltage of 1000 V for1 minute at 25° C.

Referring to the result of Table 2, the dielectric constant(ε), Q valueand temperature property (Tc) were stable even at high frequency in thisexample, while the characteristics of all the comparisons weredeteriorated.

Further, when the specimen surfaces of these examples were observedthrough a metallurgical microscope, it will be known that no void waspresent at grain boundary and a dense sintering body was constructed.

As described above, according to this example, the dielectriccomposition exhibiting high dielectric constant, high Q value and goodtemperature property, can be obtained by adding MnO₂ of 0.05-15 wt %, atleast one of 0.001-5 wt % selected from the group consisting of Bi₂O₃,PbO and Sb₂O₃ and a glass frit 0.5-15 wt % to a main component of SMZTbased on the weight of the main component and optionally further addingSiO₂ of 0.01-5 wt % and Al₂O₃ of 0.01-5 wt % and rare earth oxide of0.001-2 wt % thereto. Thus, the dielectric composition is capable of adielectric capacitor having stable characteristics and improvedreliability.

According to the method of manufacturing the ceramic capacitor, theceramic capacitor having high density and strength can be provided atthe low temperature by forming a bulk or a sheet from powder comprisinga main component of ZMZT to which MnO₂ of 0.05-15 wt %, at least one0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and aglass component of 0.5-15 wt % are added based on the weight of thecomponent, and which optionally SiO₂ of 0.01-5 wt % and Al₂O₃ of 0.01-5wt % and rare earth oxide of 0.001-2 wt % are added thereto and firingthe sheet or other resultant at 925-1080° C.

EXAMPLE 2

FIG. 2 illustrates cross-sectional structural view of a laminatedceramic capacitor in accordance with second example. The capacitorcomprises a sheet-shaped dielectric layers 11, thin internal electrodes12 and terminal electrodes 13, 14. This laminated ceramic capacitor iscomprised of eight dielectric layers 11 and seven thin internalelectrodes 12, which are alternatively laminated.

The dielectric layer 11 is made of sheet-shaped ceramic compositioncomprising a main component of SMZT to which MnO₂ of 0.05-15 wt %, atleast one of 0.001-5 wt % selected from the group consisting of Bi₂O₃,PbO and Sb₂O₃ and a glass frit(glass component) of 0.5-15 wt % are addedbased on the weight of the main component.

Alternatively, the dielectric layer 11 may include one of the dielectricceramic composition further containing SiO₂ or 0.01-5 wt % and Al₂O₃ of0.01-5 wt %, the dielectric ceramic composition further containing rareearth oxide of 0.001-2 wt %, and the dielectric ceramic compositionfurther containing SiO₂ of 0.01-5 wt %, Al₂O₃ of 0.01-5 wt % and rareearth oxide of 0.001-2 wt % is added.

The internal electrode 12 and the terminal electrodes 13, 14 include aconductive material having high reliability, for example, Cu, Ni, W andMo, or carbon, graphite or the mixture.

This laminated ceramic capacitor exhibits a stable dielectricconstant(ε), quality factor(Q) and temperature property(Tc) even in RFregion.

The method of manufacturing this laminated ceramic capacitor will bedescribed now.

Each of powdered SMZT, MnO₂, at least one selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, glass frit, SiO₂, Al₂O₃ and rareearth oxide were weighed as the predetermined amount. Each compositionwas wet-milled with water(or organic solvent such as ethanol andacetone) in ball mill for predetermined time, such as 24 hours. Theresultant mixture was dehydrated(or removal of the solvent, such asethanol and acetone) and dried. Specimens comprising differentcompositions from thereof the present invention were prepared ascomparisons(indicated by in Table 1).

Then, an appropriate amount of an organic binder was added to the driedpowder. Subsequently, the resultant powder was mixed using a mortarmachine, a mixing mill and a like to obtain a slurry having desiredviscosity. Polyvinyl alcohol(PVA) was employed as the organic binder.Other organic binder may be employed, such as ethylcellulose aqueoussolution and acryl resin solution(acryl binder).

Then, the slurry was deaired and formed into sheets through doctorblading to obtaining a ceramic green sheet. A conductive paste wasprinted as desired pattern on the green sheet. Thereby the internalelectrode layer was formed on the green sheet. The conductive paste mayinclude alloy containing at least one selected from a group consistingof Cu, Ni, W and Mo, or carbon, graphite or a mixture.

Particularly, the conductive paste employed in present invention may bea carbon paste made from a mixture powder of a carbon powder and agraphite powder, W paste and Mo paste, as well as a Cu paste, which isobtained by adding organic binder, dispersing agent, organic solventand, if necessary, reducing agent, to Cu powder and then mixing thereof.

Then, the green sheets were laminated in the thickness direction underpressure to form a laminate, followed by firing at 925-1080° C., underinert gas atmosphere, such as N₂ gas, or N₂—H₂ reductive atmosphere.Each terminal electrode was formed on the opposed sides of the laminate.Thus, the laminated ceramic capacitor can be produced through the stepof laminating alternatively the dielectric layer 11 and the internalelectrode 12.

As described above, for the laminated ceramic capacitor according tothis example, it can exhibit high dielectric constant, high Q value andgood temperature property, since it is comprised of the compositionobtained by adding MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glassfrit of 0.5-15 wt % to a main component of SMZT based on the weight ofthe component and optionally further adding 0.01-5 wt % of SiO₂ and0.01-5 wt % of Al₂O₃ and 0.001-2 wt % of rare earth oxide thereto. Thus,the laminated ceramic capacitor is capable of exhibiting stablecharacteristics and improved reliability in high frequency.

According to the method of manufacturing the laminated ceramiccapacitor, the laminated ceramic capacitor having high density andstrength can be produced by forming the internal electrode on the greensheet comprising a main component of SMZT to which MnO₂ of 0.05-15 wt %,at least one of 0.001‥4 wt % selected from the group consisting ofBi₂O₃, PbO and Sb₂O₃ and a glass component of 0.5-15 wt % are addedbased on the weight of the component, and which optionally 0.01-5 wt %of SiO₂ and 0.01-5 wt of Al₂O₃ and 0.001-2 wt % of rare earth oxide areadded thereto, laminating the green sheet in the thickness direction toform a laminate, firing the laminate at 925-1080° C. under inert gasatmosphere or N₂—H₂ reductive atmosphere. Thus, an inexpensive basemetal and carbon-based material can be used as an electrode material, inlie of a noble metal, such a Pt or Pd, since the laminated ceramiccapacitor is produced by the process of firing at relatively lowtemperature. Therefore, the manufacturing method according to thepresent invention can realize the lower cost without deteriorating thecharacteristics.

As described above, according to the dielectric ceramic composition ofthe present invention, the dielectric composition is produced by addingMnO₂ of 0.05-15 wt %, at least one 0.001-5 wt % selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃ and glass frit of 0.5-15 wt %, to amain component of SMZT based on the weight of the component andoptionally further adding 0.01-5 wt % of SiO₂ and 0.01-5 wt % of Al₂O₃and 0.001-2 wt % of rare earth oxide thereto. Thus, the dielectriccomposition can exhibit high dielectric constant, high Q value and goodtemperature property, resulting in the stable characteristics andimproved reliability at high frequency region, such as microwave.

For a ceramic capacitor, according to the present invention, thecapacitor can exhibit a low dielectric loss even at high frequencybandwidth, since it is made of the dielectric ceramic composition.Therefore, the present capacitor is suitable for RF device. The presentcapacitor can also realize the lower cost without deteriorating thecharacteristics, since an inexpensive base metal or carbon-basedmaterial can be used as an electrode material due to the low sinteringtemperature of 925-1080° C.

While the invention has been described in its preferred embodiments,this should not be construed as limitation on the scope of the presentinvention and can be modified and changed to other various embodiments.Accordingly, the scope of the present invention should be determined notby the embodiments illustrated, but by the appended claims and theirlegal equivalents. In second example, eight dielectric layers and seveninternal electrodes are laminated to form a laminate, but the number ofthe dielectric or internal electrode may be changed to be suitable forthe desired capacitor and characteristics.

What is claimed is:
 1. A dielectric ceramic composition, comprising amain component of formula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where0.8≦x<1; 0.9≦y≦1), MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃, and a glasscomponent of 0.5-15 wt %, based on the weight of the main component. 2.The dielectric ceramic composition according to claim 1, furthercomprising SiO₂ of 0.01-5 wt % and Al₂O₃ of 0.01-5 wt %.
 3. Thedielectric ceramic composition according to claim 2, further comprisinga rare earth oxide of 0.001-2 wt %.
 4. The dielectric ceramiccomposition according to claim 3, wherein the glass component isZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 5. The dielectricceramic composition according to claim 3, wherein the rare earth oxideis at least one selected from the group consisting of La₂O₃, CeO₂,Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃, HO₂O₃, Er₂O₃, Tm₂O₃, and Yb₂O₃.
 6. Aceramic capacitor comprising: a ceramic body of the dielectric ceramiccomposition according to claim 3, and electrodes formed respectively onopposed surfaces of the ceramic body.
 7. The dielectric ceramiccomposition according to claim 2, wherein the glass component isZnO—SiO₂ based glass or Li₂O-Al₂O₃—SiO₂ based glass.
 8. A ceramiccapacitor comprising: a ceramic body of the dielectric ceramiccomposition according to claim 2; and electrodes formed respectively onopposed surfaces of the ceramic body.
 9. The dielectric ceramiccomposition according to claim 1, further comprising a rare earth oxideof 0.001-2 wt %.
 10. The dielectric ceramic composition according toclaim 9, wherein the glass component is ZnO—SiO₂ based glass orLi₂O—Al₂O₃—SiO₂ based glass.
 11. The dielectric ceramic compositionaccording to claim 9, wherein the rare earth oxide is at least oneselected from the group consisting of La₂O₃, CeO₂, Pt₆O₁₁, Nd₂O₃, Sm₂O₃,Dy₂O₃, HO₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃.
 12. A ceramic capacitor comprising: aceramic body of the dielectric ceramic composition according to claim 9;and electrodes formed respectively on opposed surfaces of the ceramicbody.
 13. The dielectric ceramic composition according to claim 1,wherein the glass component is ZnO—SiO₂ based glass or Li₂O-Al₂O₃—SiO₂based glass.
 14. A ceramic capacitor comprising: a ceramic body of thedielectric ceramic composition according to claim 13; and electrodesformed respectively on opposed surfaces of the ceramic body.
 15. Aceramic capacitor comprising: a ceramic body of the dielectric ceramiccomposition according to claim 1; and electrodes formed respectively onopposed surfaces of the ceramic body.
 16. The ceramic capacitoraccording to claim 15, wherein said electrode is base metal orcarbon-based material.
 17. A ceramic capacitor comprising: a pluralityof sheets of dielectric ceramic composition according to claim 1; and aplurality of electrodes on each of sheets, wherein the sheets and theelectrodes are alternatively laminated.
 18. The ceramic capacitoraccording to claim 17, wherein said electrode is base metal orcarbon-based material.
 19. A method of producing a dielectric ceramiccomposition, comprising the steps of forming a bulk or a sheet withpowder including a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x<1; 0.9≦y≦1), to which MnO₂of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃ and glass component 0.5-15 wt % areadded based on the weight of the main component; and firing the bulk orthe sheet at 925-1080° C.
 20. The method according to claim 19, furthercomprising: providing an electrode on a main surface of the sheet;laminating the sheet in the thickness direction under pressure to form alaminate; and firing the laminate at 925-1080° C.